CHAPTER 3
How Recreation Impacts
Affect Key Characteristics
of Riparian Ecosystems
RIPARIAN RESTORATION
HOW RECREATION IMPACTS
AFFECT KEY
CHARACTERISTICS OF
RIPARIAN ECOSYSTEMS
The following paragraphs discuss recreation impacts
to soil, plant species diversity, aquatic life, and
wildlife.
Soil Moisture
Runoff and percolation patterns of natural areas
within a developed site are often changed by recreation development. Abnormally low levels of soil
moisture in certain areas and higher-than-normal
levels in others, cause plant stress. Roads that are
elevated above the natural grade can cut off water
bodies from flood plains. Roads adjacent to streams or
meadows act as levees, preventing natural flooding or
redirecting surface flow movement. Improperly
constructed roads may block or reduce water that
normally seeps or flows from the upslope to the
stream, thus reducing flow to the stream, drying out
the soil, and reducing vegetation; that is, negatively
affects the riparian ecosystem. Roads constructed
across streams or meadows can dam water and drown
vegetation on one side, and dry out vegetation on the
other side. See figures 35a and 35b.
Figure 35b—Downstream.
Pavement, structures, vehicle use, and barren soils
that result from overuse introduce more heat into the
riparian ecosystem. Added heat dries the ground,
weakens plants, and warms the water, which can
have a negative effect on aquatic species. Heat can
lead to less and less ground water availability for
plants and for recharging streams and lakes during
dry seasons and, ultimately, to aquatic and riparian
habitat loss.
Soil and Vegetation Diversity
Figure 35a—Upstream. After this dirt road was built, trees on both sides died. Trees on
the upstream side died from too much water and those on the downstream side from
too little water.
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Human foot traffic in concentrated areas can be as
destructive as cattle traffic. Horseback riding and
vehicle use, including cars, trucks, OHVs, trailers, and
mountain bicycles, also contribute to soil compaction.
See figure 36. The potential for damage increases
from human to pack stock to motorized vehicles. “A
controlled experiment on a sloping mountain grassland (Poa pratensis and Festuca idahoensis) in Montana found that 200 motorcycle passes removed twice
as much vegetation as the same number of passes by
a horse and nine times as much vegetation as 200
hiker passes” (Weaver and Dale 1978). Motorized
recreation causes “extreme and deeper soil compaction… [and] are (sic) significant agents of erosion”
(Cole as quoted in Alexander and Fairbridge 1999).
HOW RECREATION IMPACTS AFFECT KEY CHARACTERISTICS OF RIPARIAN ECOSYSTEMS
Figure 36—Damage caused by OHV use on the Ocala National Forest.
Soil compaction begins with trampling and treading,
which includes crushing, bruising, breaking, and
uprooting vegetation. See figure 37. Manning (1979)
lists a seven-step soil impact cycle that includes “the
scuffing away of leaf litter and other organic material
on the soil surface. Soil litter cover is pulverized when
exposed to trampling and is then easily blown or
washed away. ... Ordinarily, this surface material
serves to cushion layers of soil from trampling and
absorbs large amounts of rainfall. Washing [surface
runoff] of this surface exacerbates the problems of
compaction and runoff, and the cycle continues in
this manner” (Manning 1979).
Loss of vegetative cover, duff cover, and the subsequent loss of the organic horizon or topsoil by
flooding and/or by continued human disturbance,
such as trampling, exposes mineral soils. Furthermore, trampling frequently increases light intensities
and temperatures, both above and below the soil
surface (Cole as quoted in Alexander and Fairbridge
1999). Increased light intensity and temperature
disturb the physical, biological, and chemical characteristics of the soil, resulting in lower productivity and
lower water infiltration rates. See figures 38, 39, 40,
41, and 42.
Figure 37—This user-made ATV trail detours around a locked gate. It crosses one of
the few salmon-spawning streams in the area and creates edges in the riparian forest.
Figure 38—Use at this dispersed site has isolated young trees. The stump of one is
visible.
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RIPARIAN RESTORATION
Figure 39—An ever-expanding dispersed site.
Figure 40—This Alaskan trail is in a rain
forest, so it is always wet. Hikers walk on
the edges of the trail, trampling plants, ever
widening the trail, and exacerbating the
problems. The trail is also compacted,
muddy, and rutted.
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HOW RECREATION IMPACTS AFFECT KEY CHARACTERISTICS OF RIPARIAN ECOSYSTEMS
Figure 41—This dispersed parking lot is
growing because there are no boundaries.
The vegetation is becoming more and more
trampled. Angler access to the river has
caused a large chunk to erode. High flows
eventually will cause further erosion at this
vulnerable spot.
Figure 42—Windfall Lake Trailhead. There is
no defined boundary and therefore no edge
to this parking area. Parking areas with no
boundaries expand when they become
crowded or as drivers seek to park under
shade.
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RIPARIAN RESTORATION
Pore spaces in the soil aerate roots and hold water.
Compaction packs the soil particles closer together
and eliminates pore spaces (Cole as quoted in
Alexander and Fairbridge 1999). Compaction allows
less infiltration, which leads to lower soil moisture
content, fewer seeds germinating, and lower rates of
seedling survival. “Young and Gilmore (1976) found
that even when relatively high levels of organic
matter and soil nutrients were present, they may be
unavailable, perhaps due to high soil compaction and
low soil moisture and oxygen content” (Manning
1979). Reduced or eliminated pore space also weakens plant vigor and reduces root penetration. Compaction also decreases soil-building plant litter and
the number of arthropods, earthworms, and beneficial
bacteria and fungi present (Ferren and St. John 2000).
The following diagram illustrates the cumulative
effects caused by trampling and treading as vegetation
is weakened and soil is compacted. See figure 43.
Habitat Edges
The edge of a stream or the transition from riparian
ecosystem to upland forest creates a natural edge. See
figure 44. Plant type and density vary on edges as
compared to the interior, an area away from an edge.
Trails and ever-expanding camp and picnic units or
staging areas increase the exposure of the interior by
creating new edges. Roads create their own edge
effects and their impacts can be great. Longer roads
potentially have a greater impact on the nearby
environment. These edges are more open to disturbance by humans and to the influx of nonnative
species, both plant and animal, by “…providing
pathways for travel and by having newly disturbed
areas to colonize in” (Falk 2000). They encourage
nonnative wildlife species at the expense of native
species that require interior habitat for nesting and
shelter. The balance shifts, skewing the ecology.
TRAMPLING
SOIL
removal of leaf litter
loss of organic matterial
reduction in soil
macroporosity
VEGETATION
reduction of ground cover
through breakage and bruising
reduced vegetation
reduced plant vigor caused by
lack of water and nutrient availability
decrease in air and
water permeability
increased soil density causes
impedance to root extension
decrease in rain water
infiltration
exposure of roots
physical damage
to roots
increase in runoff
erosion
Figure 43—Soil/vegetation impact diagram (Manning 1979).
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increased loss
from windthrow
Figure 44—Stream edges.
Aquatic Ecosystems
Most aquatic ecosystems depend on adjacent riparian
ecosystems for food, shelter, cover, and for maintaining proper water temperature. See figure 45. When
riparian ecosystems lose structure, opportunities for
erosion and sediment deposition into water bodies
increase. See figure 46. Vehicle crossings and pollution from motorized equipment such as boats, jet
skis, and gasoline generators used for recreational instream mining also impact the aquatic ecosystems.
HOW RECREATION IMPACTS AFFECT KEY CHARACTERISTICS OF RIPARIAN ECOSYSTEMS
Fish productivity is intricately linked to riparian plant
composition. Plants provide shade to maintain proper
water temperature and shelter fish. Many aquatic
insect species spend a part of their life cycles on
riparian vegetation before dropping into the water to
be eaten by fish and other aquatic species. When
riparian vegetation is missing from the water’s edge,
much less food is available for fish and other aquatic
species.
Wildlife
Figure 45—Aquatic ecosystem. Woody debris is present; trees and shrubs overhang the
bank, creating a microclimate that helps keep the water temperature appropriate for
that stream; insects on the vegetation drop into the water to feed the fish; and the
banks are stabilized by the vegetation.
Complex structure and function, species diversity, and
age composition of riparian habitats are essential
elements for sustaining healthy wildlife populations
(McKee and others 1996). The presence of water and
rich plant diversity encourages animal diversity. Less
and/or weakened vegetation means less available
vegetative matter (structure) for animals and microbes
to use for food and shelter (Knight and Gutzwiller
1995). Wildlife also affects plant diversity because it
pollinates plants and transports seed. See figure 47.
Figure 47—Mountain goats.
The presence of humans, their paraphernalia, and
their machines affects the health of the riparian
ecosystem and the welfare of wildlife. Knight and
Cole cite four main ways that humans impact wildlife:
(1) exploitation (hunting, trapping, collection), (2)
disturbance (intentional or not; for example, wildlife
viewing, hiking through an animal’s territory), (3)
habitat modification, and (4) pollution (Knight and
Gutzwiller 1995). See figure 48.
Figure 46—Trampling and boat wakes are eroding this lakeshore.
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RIPARIAN RESTORATION
Figure 48—Partially hiding used toilet paper under a rock is not only unsightly and
unsanitary; it could also attract and sicken wildlife. It may signify ignorance about
proper waste disposal procedures and overuse of an area.
“Long-term effects of repeated disturbances range
from an increase in the population of one or more
species tolerant of human activities to the extirpation
of one or more populations” (Stanley 2000). These
disturbances affect the diversity and dynamics of the
ecosystem. Even seemingly innocuous activities such
as picnicking and wildlife viewing can have longlasting effects on wildlife. Encounters increase the
metabolism of animals, causing them to burn more
calories and expend more energy (Stanley 2000).
Although the human impact on wildlife is not well
researched, some data exists. For instance, wildlife
viewing or photography can cause animals to change
their normal behaviors. Steve Cain, senior wildlife
biologist at Grand Teton National Park, notes that
“encounters with humans increase stress on animals
that are already struggling to survive. As the fight-orflight instinct kicks in, some animals may flounder
through deep, heavy snow to get away. Even if an
animal sits still in an encounter with humans, its
metabolism is probably racing and its energy stores
are rapidly declining.
Biologists have quantified this effect using heart-rate
monitors. By some estimates, an ungulate may
expend a week’s worth of energy during a single
encounter with a human” (Berwyn 2001).
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Other examples of data concerning human impact on
wildlife are as follows:
◆ Winter recreation can be more detrimental than
warm-season recreation for wildlife because
animals are weak and stressed in the winter.
Compacted snow is deadly for small mammals,
such as voles. For example, in meadows snow
forms an insulating layer that keeps the ground
warm enough for animals to survive the winter.
When snow is compacted, it loses its insulating
value and causes the ground temperature to
drop and the animals to die. Snowmobiles are
particularly damaging to frozen shrubby
vegetation, which is brittle and snaps off when
run over. (Cole as quoted in Alexander and
Fairbridge 1999). Winter recreation can cause
loss of habitat and food.
◆ Klein (1993) found that photographers exited
their vehicles and moved closer to wildlife more
frequently than other wildlife viewers, causing
unforeseen problems such as one that Klein
(MacIvor and others 1990) points out: “Predators learn to follow the human scent trails to
nest sites” where humans had ventured (Knight
and Gutzwiller 1995).
◆ Yarmoloy and others (1988) noted that radiocollared mule deer altered their feeding and
spatial-use patterns and showed a loss in
reproductivity a year following harassment with
all-terrain vehicles (ATVs) (Knight and
Gutzwiller 1995).
Bears and their habitat are affected by human behaviors, such as recreational-use patterns and habits.
Bears have learned to associate humans and camping
with food. Rather than spend their time foraging, as
nature would have it, they seek out improperly stored
food caches for easy meals. As a result, nuisance
bears may have to be killed or be relocated from their
territories. They and other animals also are susceptible to human disease and can become ill from
exposure to trash and food left behind by humans
(Cole as quoted in Alexander and Fairbridge 1999).
See figure 49.
HOW RECREATION IMPACTS AFFECT KEY CHARACTERISTICS OF RIPARIAN ECOSYSTEMS
Figure 49—This campfire is full of nonbiodegradable trash that should have been
packed out. It may be a hazard to wildlife.
Impact Matrix
See appendix A for a matrix that summarizes potential impacts of recreation facilities and activities to
riparian forests.
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